An air filter of an air intake tract of an internal combustion engine of a motor vehicle known from the market has a filter housing comprised of a housing container and a housing cover. The housing cover is removable from the housing container for opening the filter housing. The filter housing has an inlet for air to be purified and an outlet for purified air. A round filter element is arranged in the filter housing such that it separates the inlet from the outlet. The round filter element has a filter medium for filtering the air, which surrounds the element interior with respect to an element axis in a circumferentially closed manner. The filter element is replaceably arranged in the filter housing.